High speed laser beam marking or coding of commercial products, for example, metal cans and plastic products, is a growing area of great interest and offers certain advantages over conventional marking technologies which are generally afflicted with one or more drawbacks. For example, marking by ink jet printing requires frequent maintenance to keep the nozzle from clogging. Further, the use of fluids such as ink jet inks containing solvents in contact with the printed surface cannot be tolerated in certain critical applications for reasons related to safety and compatibility.
In view of the foregoing, laser beam marking systems have received a significant attention from the industry. See, for example, European Patent Application 0 739 933 Al, UK Patent Application GB 2291719 A, and U.S. Pat. Nos. 5,760,120 and 4,861,620. Laser beam marking has the advantage that a fluid is not employed in the marking process. The laser beam marking systems can also be operated with minimal maintenance requirements. However, systems known heretofore suffer from certain shortcomings. For example, in some systems, a polymeric molded product containing a laser sensitive pigment is marked by irradiating with a laser beam. The laser beam creates a mark by evaporating or pyrolyzing the polymeric resin, and, as a result, exposing the pigment. See, e.g., European Patent Application 0 739 933 A1 and U.S. Pat. No. 5,760,120. Such a system, however, can leave behind dust or residues as the polymer material is ablated from the surface of the product. Further, in the above method, since the polymer is etched by the laser beam, the surface of the product is uneven, and, therefore, lacks smoothness.
Thus, there exists a need for a laser marking system that does not create or leave behind dust or residue during marking. There further exists a need for a laser marking system that leaves a relatively smooth surface. There further exists a need for a system that offers a broad range of color contrast. There further exists a need for a system that is amenable in a variety of colors. There further exists a need for a laser marking system that can mark at high speeds, for example, at about 300 feet/minute or higher.
These and other objects of the present invention will be apparent from the detailed description of the preferred embodiments of the invention set forth below.